Optical encoder

ABSTRACT

An optical encoder that accurately performs rotation while protecting a rotating disk from dust. The optical encoder comprises a shaft ( 5 ) supported by a bearing ( 6 ) in a housing ( 1 ), a rotating disk ( 8 ) fixed to the shaft ( 5 ), a light-emitting element ( 10 ) mounted on the housing ( 1 ), a photodetector element ( 12 ) mounted on a sub-board supported by the housing ( 1 ) for receiving the light passing through or reflected by the rotating disk ( 8 ), and a main substrate ( 13 ) mounted on the housing and provided with a circuit for determining the quantity of rotation or the angular position form the light received by the photodetector element ( 12 ). The housing ( 1 ) includes a holder ( 9 ), which as an annular cover ( 9   a ) engaged with the border of the main substrate ( 13 ) and a retainer ( 9   b ) formed on the cover ( 9   a ) for holding the light-emitting element.

FIELD OF THE INVENTION

The present invention relates to an optical encoder for detecting therotations of a motor, etc.

BACKGROUND OF THE INVENTION

A prior art optical encoder is constructed as shown in FIG. 2 and FIG. 3

In the drawings; housing 20 is attached to and fixed at a mount 23 of abracket 22 of a motor 21. A rotating shaft 24 is supported at thehousing 20 by means of a bearing 25 and is directly connected to therotating shaft 26 of the motor 21 via a connector 26 a. A rotary disk 27has a pattern (not illustrated) composed of a light shielding portion ora light-penetrating portion attached to a transparent member such asglass that is attached to the rotating shaft 24. A holder 28 is a holderto retain light emitting elements, which is constructed by molding. Asshown in FIG. 3, the holder 28 is constructed of a supporting portion 28a attached to the housing 20 and an attaching portion that attaches thelight-emitting element 29. The light emitting element 29 is attached soas to be inserted into a hole portion secured at the supporting portion28 a of the holder 28. A sub-board 30 has a photo detector element 31attached to the plate surface of the sub-board 30. A main board 32 isattached to the housing 20 via a supporting member (not illustrated),and the main board is connected to the sub-board 31 by a connection line(not illustrated), and an electronic component that detects the speed ofrotation or position of the rotation is incorporated on the platesurface of the main board 32. A cover 33 covers up the optical encoderand is fixed at the bracket 22 of the motor 21. A lead wire 34 comes outof the optical encoder.

Next, a description is given of an assembly process of an opticalencoder.

First, the rotating shaft 24 is attached to the bearing 25 attached tothe housing 20, and a rotary disk 27 is fixed at the rotating shaft 24.Next, the sub-board 30 provided with the photo detector element 31 isattached to the housing 20, wherein the holder 28 to which the lightemitting element 29 is attached is fixed at the housing 20 so that it isopposed to the photo detector element 31 to accommodate the rotary disk27 therein.

The optical encoder thus constructed is completed so that the cover 33surrounding the optical encoder is attached to the bracket 22 of themotor 21 after it is attached on the mounting seat of the bracket 22.

Actually however, since the outer circumferential portion of the rotarydisk is made open until the prior art optical encoder is attached to themotor, foreign substances and dust floating in the air may adhere to therotary disk or foreign substances and/or dust adhered to the cover maydrop from the cover due to vibrations during operation and adhere to therotary disk, thereby making rotation detection impossible.

DISCLOSURE OF THE INVENTION

It is therefore an object of the present invention to provide an opticalencoder that is capable of executing accurate rotation detection, freefrom any adhered foreign substances and/or dust.

In order to solve the abovementioned problems, an optical encoderaccording to the invention comprises a rotating shaft pivotallysupported on a bearing of the housing; a rotary disk fixed at therotating shaft; a light emitting element attached to the housing; aphoto detector element attached to the housing, which can receive lightpassed through or reflected by the rotary disk from the light emittingelement; and a main board incorporating a circuit that detects the speedof rotation and position of rotation from the light received by thephoto detector element and is attached to the housing; wherein a holderconsisting of a covering portion annularly formed so as to be engagedwith the outer circumference of the main board and a light emittingelement retaining portion formed at the covering portion is attached tothe housing.

Therefore, according to the invention, it is possible to secure adust-proof structure without hindering the assembly process of anoptical encoder and to accurately detect the rotation without permittingforeign substances and/or dust to adhere to the rotary disk.

BRIEF DESCRIPTION OF THE DRAWING

FIG. 1 shows an embodiment of the invention, wherein (a) is a sideelevational view of an optical encoder, and (b) is an enlarged view ofthe major parts of the optical encoder,

FIG. 2 is a side elevational view of a prior art optical encoder, and

FIG. 3 is an enlarged view of the major parts of the prior art opticalencoder.

BEST MODE FOR CARRYING OUT THE INVENTION

Hereinafter, a description is given of an embodiment of the inventionwith reference to the accompanying drawings:

FIG. 1 shows. an embodiment of the invention, wherein (a) is a sideelevational view of an optical encoder, and (b) is a perspective view ofthe holder thereof.

In the drawings, a housing 1 is attached to a mount 4 secured on abracket 3 of a motor 2. A rotating shaft 5 is attached to the housing 1via a bearing 6. The rotating shaft 5 and a rotating shaft 7 of themotor 2 are connected to each other by means of a connector 7 a. Arotary disk 8 has a pattern (not illustrated) consisting of a lightshielding portion and a light penetrating portion on a transparentmember such as glass, which is attached to the rotating shaft 5. A lightemitting element holder 9 is provided with a covering portion 9 aannularly formed of synthetic resin as shown in FIG. 1b and a lightemitting element retaining portion 9 b that retains the light emittingelement 10. The light emitting element 10 is attached so as to beinserted into a hole portion secured at the light emitting elementretaining portion 9 b. A sub-board 11 has a photo detector element 12formed on the plate surface thereof and is attached to the housing 1. Amain board 13 is attached to the housing 1 by means of a supportingmember (not illustrated), wherein the main board 13 and the sub-board 13are connected to each other via a connector (not illustrated), and anelectronic component that detects the speed of rotation or position ofrotation is mounted on the plate surface of the main substrate 13. Acover 14 covers up the optical encoder and is fixed on the bracket 3 ofthe motor 2. A lead wire 15 is provided to lead the amount of rotationand the position thereof from the optical encoder.

Next, a description is given of an assembly process of an opticalencoder.

The rotating shaft 5 is attached to the bearing 6 attached to thehousing 1, and the rotary disk 8 is fixed at the rotating shaft 5. And,the sub-board 11 provided with the photo detector element 12 is fixed atthe housing 1. The main board 13 is fixed at the housing 1 by means of asupporting member (not illustrated). As one side of the covering portion9 a of the holder 9 is fitted to the outer circumference of the mainboard 13, the other side of the covering portion 9 a is brought intocontact with the plate surface of the housing 1. A light emittingelement 10 is attached into the hole of the light emitting elementretaining portion 9 b of the holder 9, thereby constituting the opticalencoder. The housing of the optical encoder thus constructed is fixed atthe mount 4 secured at the bracket 3 of the motor 2, wherein therotating shaft of the optical encoder is coupled to and fixed at therotating shaft 7 of the motor 2 via a connector 7 a. Thereafter, thecover 14 that surrounds the optical encoder is constructed so as to beattached to the bracket 3 of the motor 2. Therefore, since the holder 9that retains the light emitting element 10 surrounds the outercircumference of the rotary disk 8 secured between the housing 1 and themain board 13, no foreign substances and/or dust are permitted to enterthe rotary disk 8, and rotation can be accurately detected.

Industrial Applicability

Also, as described above, since one side of the covering portion 9 a ofthe holder 9 is devised to be fitted to the outter circumferentialsurface of the main board 13 until the other side of the coveringportion 9 a is brought into contact with the plate surface of thehousing 1 when attaching the holder 9, it is possible to attach theholder 9 around the final process of the final assembling of an opticalencoder, and in particular the existence of the covering portion 9 a ofthe holder 9 will not hinder the assembly process.

What is claimed is:
 1. An optical encoder comprising: a housing; arotating shaft pivotally supported on a bearing of the housing; a rotarydisk fixed to said rotating shaft adjacent to said housing; a lightemitting element sending light to a photo detector element via saidrotary disk; a main board mounted adjacent to said housing, said mainboard including a circuit that detects an amount of rotations and aposition of rotation of the rotary disk from the light received by saidphoto detector element; and a holder attached to said housing andfurther comprising a covering portion annularly formed so as to beengaged with an outer circumferential surface or edge of said main boardand a light emitting element retaining portion formed at the coveringportion.
 2. The optical encoder of claim 1, wherein the covering portioncomprises an annular band.
 3. The optical encoder of claim 2, whereinthe annular band is open.
 4. The optical encoder of claim 2, wherein: ahousing surface of the housing is disposed generally parallel to themain board; the annular band substantially encloses a space between thehousing surface and the main board; and the space contains the rotarydisk.
 5. The optical encoder of claim 1, wherein the holder is unitaryand the covering portion and the light emitting element retainingportion comprise respective portions of the unitary holder.
 6. Theoptical encoder of claim 5, wherein the holder is formed of syntheticresin.
 7. The optical encoder of claim 1, wherein the engagement of thecovering portion with the outer circumferential surface of said mainboard includes direct contact.